Tripping Limit switch conundrum - http://www.hvacmechanic.com/ Forums
Original message
| tmohapp
 |  "Tripping Limit switch conundrum"
, posted Fri 19 Sep 12:30  
I have a 100,000 btu Tempstar downdraft gas furnace installed in a horizontal position in a crawl space. It was installed in 1998 and other than having a combustion blower assembly that fell apart has been relatively trouble free. It is a high efficiency with outside intake and exhaust vents. This past spring I noticed it started blowing cold air. I called the service center and because I live in a rural area that can be hard to access with heavy snow they told me to try some things. What fixed the problem temporarily was to reset the limit switch button for the switch in the combustion chamber. That worked for two weeks and it happened again. I again reset the switch, was fine for 3 days and it recurred. After the snow had melted I had the serviceman up and he replaced the limit switch, checked the gas pressures, cleaned the pilot and burners, etc. As he pulled out of my driveway it happened again. He came back and thought it might be the smart valve, which was replaced ($$$!). The problem continues. I had a different serviceman up thinking he'd have some fresh ideas, he checked everything out and can't see a reason for the problem.....Any help would be appreciated before the snows come back again....
Tom
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Replies:
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| tmohapp
| "Re(1):Tripping Limit switch conundrum" , posted Sat 20 Sep 09:18
Thanks learner, yes the filters are changed regularly and the blower was an exact replacement. Also thank you Yuri, so you believe the heat exchanger may have a crack in it? Would I expect my CO detector to be going off? Also, if it is the heat exchanger, is that the end of this unit, seems like that's and expensive part to fix? It also seems like 10 years isn't much of a life span for such an expensive and important home appliance....
Tom
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| learner
| "Re(1):Tripping Limit switch conundrum" , posted Fri 19 Sep 17:49
Hi,
I am no expert but limit switch itself can go bad. Or blower is not extracting hot air from combustion chamber causing a temp. rise within the unit. As simple as dirty filter can cause this. Was the blower assembly exact replacement?
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| | yuri
| "Re(2):Tripping Limit switch conundrum" , posted Fri 19 Sep 19:20:
If it has a red reset button and is near the burners it sounds like the flame rollout switch. That is a VERY serious problem if it trips. ICP had LOTS of problems with faulty heat exchangers/rivets popping and yours may be one of them. Get your tech to cut an access hole in the hot air bonnet and look at the heat ex for problems. An experienced guy will know where to check those units. I really dislike those units, lots of Smartvalve problems etc etc. I would install a Lennox G51MP (multiposition) and it will be a lot more reliable especially if it is hard to get quick service in your area. Or get yourself a good woodburning stove for backup.
Yuri
[this message was edited by yuri on Fri 19 Sep 19:24] |
| | yuri
| "Re(3):Tripping Limit switch conundrum" , posted Sat 20 Sep 10:19
IMO they were not built well to start with. Seen lots of them with cracks/popped compression rivets. Lots changed under warranty. Labor to change it will be $600 and over. I would invest my $$ in a new furnace with new parts and a warranty. That one is a money pit IMO. I have a G51 and they have been out for 6 or more yrs and are tried and proven. Good meat and potatoes furnace. There is a more expensive G61V if you are interested in something better.
Yuri
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